In electric power transmission and distribution networks, fault current conditions may occur. A fault current condition is an abrupt surge in the current flowing through the network caused by faults or short circuits in the network. Causes of the faults may include lightning striking the network, and downing and grounding of the transmission power lines due to severe weather or falling trees. When faults occur, a large load appears instantaneously. This surge or fault current condition is undesirable as the condition may damage the network or equipment connected to the network. In particular, the network and the equipment connected thereto may burn or, in some cases, explode. The network, in response, delivers a large amount of current (i.e. overcurrent) to this load or, in this case, the faults.
A fault current limiter (FCL) is a device for limiting fault currents, such as in a power system. Various types of FCLs have been developed over the years, including superconducting fault current limiters (SCFCLs), solid state fault current limiters, inductive fault current limiters, as well as other varieties known in the art. The FCL may be implemented in a system having generation, transmission, and distribution networks for providing power to various industrial, commercial, and/or residential electrical loads.
Generally, the SCFCL comprises a superconducting circuit exhibiting almost zero resistivity below a critical temperature level TC, a critical magnetic field level HC, and a critical current level IC. If at least one of the conditions is raised above the critical level, the circuit becomes quenched and exhibits resistivity. During normal operation, the superconducting circuit of the SCFCL system is maintained below TC, HC, and IC. During a fault, one or more the conditions is raised above the critical level TC, HC, and IC. Instantaneously, the superconducting circuit in the SCFCL system is quenched and resistance surges, thus limiting transmission of the fault current. Following some time delay and after the short circuit fault is cleared, To, Ho and Io are returned to normal values and current is transmitted through the network and the SCFCL system.
The SCFCL may comprise an enclosure electrically decoupled from ground, so the enclosure is electrically isolated from ground potential. In other embodiments, the enclosure may be grounded. The SCFCL may also have first and second terminals electrically connected to one or more current carrying lines. Maintaining the superconducting circuit at a low temperature within the enclosure using, for example, a coolant such as liquid nitrogen or another cryogenic gas may be desirable. Yet during a fault, voltage starts to build up across the superconducting circuit, creating gaseous bubbles (e.g., nitrogen) inside the enclosure. The bubbles weaken the dielectric strength of the coolant. Increasing a physical clearance between the superconducting circuit within the enclosure and the walls of the enclosure helps to increase the high voltage capability (dielectric strength) of the unit to overcome the deficiencies created by bubbles. Still, increasing the overall size of the enclosure is undesirable.
With respect to these and other considerations the present disclosure is provided.